1. Technical Field of the Invention
The present invention relates to a focal plane shutter apparatus, more concretely to a focal plane shutter apparatus assembled particularly in a digital camera which is required to reduce an amount of abrasion powder generated by the sliding of components as much as possible.
2. Prior Art
A focal plane shutter apparatus is composed of a plurality of light shielding blades, a dowel caulked or otherwise integrally attached to each blade, and an arm which is slidably engaged with the dowel to open or close each blade.
Herein below listed are patent documents of the prior art. Patent Document 1 is Japanese Patent Application Laid-Open No. 2001-157087. Patent Document 2 is Japanese Patent Application Laid-Open No. 2001-311997. Patent Document 3 is Japanese Patent Application Laid-Open No. 2002-010137.
When the blades are opened and closed, the arm and dowel frictionally slide with each other and abrasion powder is generated. In a conventional camera using a silver film, the film is wound up every exposure operation, and therefore the abrasion powder generated in the focal plane shutter apparatus assembled in the camera is not accumulated. However, in a digital camera, image pickup devices such as CCD are used instead of the silver film. When the focal plane shutter apparatus assembled in the digital camera is repeatedly driven, the abrasion powder is generated by the rubbing of the arm and dowel with the open or close operation of the blades. When the abrasion powder is accumulated in an imaging frame, picture quality is lowered, and this is a problem to be solved.
It is to be noted that several abrasion powder countermeasures have heretofore been proposed. For example, in Patent Document 1, an image pickup apparatus has been proposed which is equipped with a dust mode for detecting foreign materials on the CCD and a cleaning mode for cleaning the foreign materials. These modes can quickly be switched. When the foreign materials on the CCD are detected and indicated in the dust mode, the mode quickly shifts to the cleaning mode, and a cleaning operation can be performed.
In Patent Document 2, an electronic camera has been proposed in which an optical low pass filter is inserted between a focal plane shutter and an image pickup device. This low pass filter prevents an image quality from being deteriorated by the abrasion powder generated from the focal plane shutter.
Further in Patent Document 3, an electronic camera has been proposed in which the low pass filter can be moved during an exposure operation. Even when dust is attached to the low pass filter, the filter is moved during the exposure operation, the shadow of the dust is dispersed into a plurality of pixels, and the quality of the image obtained by the image pickup device is prevented from being deteriorated. However, any of these abrasion powder countermeasures is devised on the fact that the abrasion powder is generated, and is not a fundamental countermeasure to eliminate the abrasion powder itself.